Exploratory Drilling for High-Speed Rail Tunnel
The planned California High-Speed Rail will be the first high-speed rail system in the country, connecting major metropolitan areas at speeds of over 200 miles per hour. The Palmdale-to-Burbank section of the project includes proposed route alternatives that tunnel through the geologically complex San Gabriel Mountains. Available geotechnical information was limited, but indicated potential faults and rock shearing.
California High Speed Rail Authority
Crux collected over 8,400 feet of rock core in the complex conditions. Borings had to be drilled at inclined angles to intersect and gather information about the dominant fault traces and associated groundwater. Packer testing, groundwater sampling, and hydraulic jacking were completed as directed, and vibrating wire piezometers were installed and tailored to the rock conditions.
As anticipated, faults were encountered in multiple borings. The combination of weakened ground and the depth of the boreholes made it difficult to use typical installation methods. To mediate this, Crux developed an installation solution that bundled piezometers and tremie pipes into a grouting shoe at preselected depths. The grouting shoe was then lowered to its final depth using a sacrificial wireline.
All drilling operations took place within the Angeles National Forest and were subject to environmental regulations. A combination of Forest Service roads and helicopter support was used to mobilize, access boring locations, and transport core samples. Additionally, Crux developed a water loss system to comply with USFS requirements, which allowed crews to monitor and identify water loss while drilling.
Completing multiple, deep cores within a federally protected area required innovative techniques to minimize impacts and maximize efficiency. All drilling and instrumentation was successfully completed, and will assist in determining the feasibility of the rail tunneling through the San Gabriel Mountains.